The radio spectrum includes a number of regulated frequencies and frequency bands that are allocated to various communications. For example, cellular telephones, AM radio, FM radio, and broadcast television services use different frequency bands for transmissions. Companies, such as cellular telephone providers, may license portions of designated frequency bands for communications. The licenses may cover only a particular geographic area so that the same frequency bands may be used by different users in different regions.
Because frequency bands are allocated to particular users, spectrum holes frequently form. A spectrum hole occurs when frequencies that have been assigned to a primary user are not being used by that user at a particular time. Spectrum holes cause less efficient use of the wireless spectrum. Cognitive radio networks attempt to make use of spectrum holes that are not being used by a primary user by dynamically configuring radios to detect inactive channels. These inactive channels can then be assigned to a secondary user until the primary user returns. Once a primary user returns, the secondary user may wait or transition to other inactive channels in a process referred to as spectrum handoff. Determining when and how to enable spectrum handoff in cognitive radio networks with multimedia applications presents challenges due to multiple interruptions from primary users and contentions among secondary users. Switching channels when using multimedia applications can lead to interrupted video streams. Transmitting multimedia applications over cognitive radio networks therefore can lead to a lack of a smooth video delivery when a user expects real-time transmission.
Within wireless networks, multimedia transmissions may also be sent that have differing priorities. For example, a video that a user wants to download for later use need not be delivered at a sufficient speed to allow real-time streaming playback. On the other hand, a multimedia transmission in a military application may need to be delivered without any delay and at very high resolution to aid strategic battlefield decisions. Smooth spectrum handoff and efficient spectrum management may provide acceptable multimedia transmission over cognitive radio networks.